This application relates to materials suitable for use in articles directed to absorbing body fluids. The application particularly relates to materials capable of rapidly acquiring aqueous fluids (e.g., urine, menses, etc.) and preferably releasing such fluids to fluid distribution and storage materials.
The development of highly absorbent articles for use as disposable diapers, adult incontinence pads and briefs, and catamenial products such as sanitary napkins is the subject of substantial commercial interest. The ability to provide high performance absorbent articles such as diapers has been contingent on the ability to develop relatively absorbent cores or structures that can acquire, distribute and store large quantities of discharged body fluids, in particular urine where a wearer may expel a large quantity of fluid very quickly (typically called a xe2x80x9cgushxe2x80x9d) and, at the sane time, provide desirable fluid handling properties so as to keep the wearer""s skin dry and comfortable. These three functions can be accommodated by specific portions of the absorbent articles optimized for each. An acquisition material (or layer) is designed to take in fluid rapidly during a gush. The acquisition material also has sufficient capillary pressure to pull residual fluid away from adjacent layers (e.g., a topsheet). The gush fluid is stabilized prior to being given up to the distribution material. An optional distribution material (or layer) has sufficient capillary pressure (described in more detail below) to pull fluid away from the acquisition member and distribute it toward the front and rear of the absorbent article, often against the force of gravity to a height of 10-20 cm according to the size of the core. The storage member (or layer) has the highest capillary pressure and may comprise hydrogel-forming absorbent polymers or HIPE-derived hydrophilic absorbent foams to pull the fluid away from any distribution layer that may be present and store the fluid xe2x80x9cpermanentlyxe2x80x9d away from the skin of the wearer.
Significant effort has been devoted towards the development of superior fluid acquisition and storage components. For example, U.S. Pat. No. 4,898,642 (Moore et al.) issued Feb. 6, 1990, U.S. Pat. No. 4,888,093 (Dean et al.) issued Dec. 19, 1989, U.S. Pat. No. 5,137,537 (Herron et al.), U.S. Pat. No. 5,217,445 (Young et al.), issued Jun. 8, 1993, and U.S. Pat. No. 4,822,453 (Dean et al.) describe curly, stiffened fibers that, when formed into low density webs, do not collapse when wet and retain their ability to acquire fluids at high rates as is experienced in a xe2x80x9cgushxe2x80x9d situation during urine voiding. Certain types of polymeric foams have been used in absorbent articles for the purpose of actually imbibing, wicking and/or retaining aqueous body fluids. See, for example, U.S. Pat. No. 3,563,243 (Lindquist), issued Feb. 6, 1971 (absorbent pad for diapers and the like where the primary absorbent is a hydrophilic polyurethane foam sheet); U.S. Pat. No. 4,554,297 (Dabi), issued Nov. 19, 1985 (body fluid absorbing cellular polymers that can be used in diapers or catamenial products); U.S. Pat. No. 4,740,520 (Garvey et al.), issued Apr. 26, 1988 (absorbent composite structure such as diapers, feminine care products and the like that contain sponge absorbents made from certain types of super-wicking, crosslinked polyurethane foams). U.S. Pat. No. 5,563,179 (Stone et al.) issued Oct. 8, 1996, describes hydrophilic absorbent foams useful for acquiring and distributing aqueous fluids in, e.g., absorbent cores. Similarly, various nonwoven materials have been proposed for fluid acquisition. Of key importance is the ability of these materials to acquire fluids repeatedly in use, to survive storage in a compressed state, and to release the acquired fluid to a subsequent fluid distribution or storage material.
The desirability of reducing the bulk of an absorbent article in the crotch area thereof is also well known. For example commonly assigned U.S. Pat. No. 5,549,589, issued to Horney, et al. on Aug. 27, 1996, commonly assigned U.S. Pat. No. 5,800,416, issued to Seger, et al. on Sep. 1, 1998, and copending, commonly assigned U.S. patent application Ser. No. 08/825,072, filed Mar. 27, 1997 by G. Young et al., Ser. No. 08/825,071, filed Mar. 27, 1997 by G. LaVon et al., and Ser. No. 08/826,208, filed Mar. 27, 1997 by G. Young et al. are all directed to materials that distribute acquired body fluids from the crotch area of an absorbent article to other parts of the absorbent article which allows a reduction in crotch size.
The art has also recognized the desirability of keeping the crotch area of an absorbent article as thin as possible.
U.S. Pat. No. 5,779,860, issued to Hollenberg, et al. on Jul. 14, 1998 describes through air dried tissue structures that are said to expand substantially when wetted. The tissue structures comprise chemithermomechanical pulp and a wet strength resin and are calendered to significantly increase density and reduce caliper. While the ""860 patent states that the calendered web can increase in caliper 200 to 600% when fully wetted or saturated, such increased caliper is determined by saturating the web with no confining pressure, drying the web, and measuring the caliper of the dried web. While such increases may be substantial, they are not predictive of the performance of a material useful as a component of a core in an absorbent article where any fluid insult will typically happen while the core is under pressure (e.g., due to the wearer sitting or lying down). Such wearer-applied pressure results in a need to expand against such a confining pressure.
U.S. Pat. No. 5,877,097, issued to West, et al. on Mar. 2, 1999 describes densified webs comprising cellulose fibers and a bonding agent that are formed at a low density and compressed to a higher density. The webs are said to have an absorbent capacity that is superior to prior densified and bonded webs. While such webs may have superior absorbent capacity (on a gram of fluid/gram of absorbent basis), there is no indication that the webs can acquire such fluids quickly enough for use as an acquisition member or that such webs would be able to release acquired fluids to other components for ultimate storage.
The art has also considered sponges as an expansive absorbent medium. For example, a sanitary napkin is described in U.S. Pat. No. 3,512,530, issued to Jones on May 19, 1970, where a compressed regenerated cellulose sponge layer is bonded to a larger fibrous cellulose layer to form a multi-ply absorbent core. The compressed regenerated cellulose sponge layer is positioned over the fibrous layer, and it is typically centered about it; it is intended as the primary absorbent element of the sanitary napkin, while the fibrous layer acts as a secondary or back up absorber. The sanitary napkin described therein is said to be thin prior to use, as compared to other sanitary products having the same absorbent capacity. However, because the sponge layer is intended to provide the primary absorbent capacity, fluid would only wick into the backup fibrous layer after the sponge is substantially saturated with resulting risk of rewet because the underlying layer does not absorb fluid from the sponges.
In another use of sponges, EP Patent 293 208 B1, granted to the Lion Corporation on Jul. 24, 1991, describes the use of multiple layers of compressed regenerated cellulose sponge sheets in a sanitary napkin as the sole absorbent material. Because the sponge serves as the sole absorbent material in the sanitary napkin, the focus is on providing multiple layers of sponge material for softness and there is no recognition therein of the importance of the fluid handling properties that are necessary for a material to be suitable for use as an acquisition material in an absorbent article.
There have also been several attempts to create a fluid-activated acquisition zone in absorbent articles by taking advantage of the swelling of hydrogel-forming absorbent polymers in an inhomogeneous structure to create void volume. See for example PCT Application Serial No. WO 97/34559, published in the name of Lash et. al. on Nov. 19, 1997 and U.S. Pat. No. 5,855,572, issued to Schmidt on Jan. 5, 1999. Such structures are, however, not effective during the first loading of the article because the swelling of hydrogel-forming polymers is too slow to rapidly acquire the deposited bodily fluids, such as urine, and, therefore, only provide void space for subsequent gushes. Further, the void volume provided by such structures does not contain fibers to temporarily immobilize the deposited fluid for subsequent absorption by other core components.
Other examples of absorbent structures including expansive components include U.S. Pat. No. 3,736,931, issued to Glassman on Jun. 5, 1973, which discloses a sanitary napkin having an outer layer of a soft nonwoven moisture absorbent material and an inner layer of a highly compressed fluid absorbent material (the compressed material is not described in any greater detail) with a layer of impervious material therebetween. The napkin preferably is V-shaped in cross section. When the napkin is worn, menses is first absorbed by the compressed layer. Swelling of the compressed layer caused by such absorption is said to expand the outer non-compressed layer thereby adjusting the sanitary napkin to each wearer. In this structure, the compressed layer becomes substantially saturated before absorption of fluids by other layers because of the impervious material that is located between the two absorbent layers. That is, fluid is not substantially pulled away from the compressed layer into another for further distribution and there is a substantial risk of rewet as the compressed layer becomes saturated.
Another example of a compressed absorbent material that is said to expand rapidly on insult, can be found in PCT application WO 99/32060 published in the name of Kimberly-Clark Worldwide, Inc., on Jul. 1, 1999. Described therein are fibrous carded or air laid webs which include a binder. The fibers comprise a blend of cellulosic (rayon or cotton) fibers and non-cellulosic (polyolefin, polyester, and polyamide) and the binder is said to be moisture sensitive and can comprise hydrogen bonding, a non-aqueous solution, a powder, or a material in a fibrous form. The ""060 application indicates that the web is compressed to a density of up to about 0.3 g/cc and further indicates that, when wetted, the web should expand rapidly to greater than 80% of its uncompressed thickness. While desirable properties and objectives are described in the ""060 application, the application gives no indication that such properties can be achieved. For example, it is known that densification can permanently rearrange fibers to a higher density configuration and the application fails to indicate that the densified webs described therein actually expand rapidly to a lower density. Rather it indicates that the webs are formed at a lower density, densified and that the densified webs should expand rapidly.
Thus, there is a need for materials that are thin and of low bulk for use as core components in absorbent articles. There is a further need for such materials to have useful fluid handling properties that are suitable for a particular use. For materials that are intended for use as an acquisition component in the core of an absorbent article there is a need for materials that can acquire aqueous fluids quickly and that readily xe2x80x9cgive upxe2x80x9d such fluids to other core components while the material is under a confining pressure. There is a further need for such materials to be soft and body conforming to provide fit and comfort. There is also a continuing need for improved absorbent articles that make use of such materials.
The present invention comprises a thin until wet material that is particularly useful for use as an acquisition member of an absorbent article (e.g., diapers, catamenial products, and adult incontinence devices). Suitable materials according to the present invention include fibrous assemblies that utilize wet strength means to stabilize the assembly and compressed sponges. The material is further provided with a temporary binding means to hold it in a thin state until it is exposed to an aqueous fluid. When the material is exposed to an aqueous fluid, the temporary binding means releases and the thin until wet material can expand to the expanded wet density. When the material is saturated with an aqueous fluid it has an expanded wet density of between about 0.04 grams/cm3 and about 0.4 grams/cm3 and an expanded capillary desorption height of less than about 25 cm and a temporary binding means that helps maintain the web at a compressed dry density between about 0.06 grams/cm3 and about 1.2 grams/cm3 until the material is exposed to an aqueous fluid. The ratio of the compressed dry density, to the expanded wet density is also greater than about 1.5:1. Crosslinked cellulose fibers are particularly preferred fibers for use in the fibrous assembly. The fibrous assembly may further comprise high surface area cellulosic fibers and/or resilient synthetic fibers. Particularly preferred wet strength means comprise papermaking wet strength resins. Particularly preferred temporary binding means for the fibrous assembly comprise a water soluble/water dispersible polymer. Preferred sponges comprise compressed regenerated cellulosic sponges.
A preferred process for making the fibrous webs comprises wet laying the fibrous assembly in the presence of a wet strength means; drying the wet laid nascent thin until wet web; providing the nascent thin until wet material with temporary binding means; densifying the nascent thin until wet material to a compressed dry density; and activating the temporary binding means to help maintain the densified structure. Preferably, the densified structure is further processed to increase the softness thereof.
The process for providing sponge-based thin until wet materials comprises producing a regenerated cellulosic sponge using means known to the art. Once the sponge has been formed, it is dried and compressed to a predetermined density using heated compression means.
The present invention further provides absorbent structures suitable for use in absorbent articles, such as diapers, incontinent briefs, training pants, diaper holders and liners, feminine hygiene garments, and the like, designed to provide improved fit and comfort for the wearer while adequately containing body exudates. Such an absorbent article typically comprises a liquid pervious topsheet, a substantially liquid impervious backsheet, and an absorbent core disposed between the topsheet and the backsheet. The absorbent core is designed so as to be relatively narrow and thin in the crotch area, even when the core absorbs significant amounts of fluid during use. To achieve this, the absorbent core is designed such that absorbed fluid is moved substantially from the crotch region to the front and/or rear waist regions of the article and further comprises the thin-until-wet acquisition material of the present invention.